Field of the Invention
The present invention relates to a method for manufacturing a semiconductor device, and more particularly, to a method for bonding a substrate and a semiconductor element in a semiconductor device.
Description of the Background Art
In recent times, high-efficiency and energy-saving semiconductor devices with consideration for environmental problems grow in demand due to increasing environmental controls. The semiconductor devices are used for industrial equipment, drive control equipment of household electrical appliances including motors, vehicle-mounted control equipment for electric-powered vehicles and hybrid vehicles, railroad control equipment, and control equipment for solar-electric power generation, for example. The semiconductor devices need to be suitable for high electric power.
Particularly for the vehicle-mounted control equipment and the railroad control equipment, the semiconductor devices can be used under heavy load conditions (under high temperature conditions) from the viewpoint of saving energy and suppressing electrical-energy conversion losses. In other words, high-efficiency and low-loss operations are needed under the high temperature conditions. Specifically, normal operating temperatures (junction temperatures) have been 125° C. to 150° C., but operations under high temperature conditions at 175° C. to 200° C. or higher will be required.
Thus, materials for semiconductor modules and structures thereof need to be reconsidered to suppress switching losses reduce losses, and increase efficiency under the high temperature conditions. Wiring connected portions (bonding portions) in the semiconductor devices in particular deteriorate most easily, and achieving high quality, high reliability, and extended lifetime of the wiring connected portions is a great challenge. Moreover, costs of expensive materials having sinterability need to be reduced.
Bonding materials having sinterability have recently been developed, but the application to products makes it difficult to suppress the costs and maintain quality and reliability of bonding.
Conventional bonding materials having the sinterability, which are paste, are screen-printed with masks or applied with syringes. Thus, the bonding materials do not have a uniform thickness, and irregularities are formed on a surface of the bonding materials.
The bonding materials having the sinterability are more expensive than solder materials. For example, when a bonding material is disposed by screen printing, part of the bonding material goes to waste.
When the bonding material is extruded from a bonding surface to which a semiconductor element is bonded, pressure fails to be applied to part of the bonding material during sintering, so that a sintered material to which pressure is not applied may fall off after sintering.
After a pasty bonding material is conventionally disposed and dried, the semiconductor element is disposed on the bonding material. Thus, the semiconductor element may sometimes be damaged when the semiconductor element is disposed, and the semiconductor element may sometimes be misaligned in subsequent steps.